crypto/x509: checkSignature why the loop doesn't `break` after finding `algo`?

[dchaofei]

What version of Go are you using (go version)?

$ go version
go version go1.18 darwin/amd64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOVERSION="go1.18"

What did you do?

I read the go source code and found a performance issue, checkSignature why the loop doesn't break after finding algo?

go/src/crypto/x509/x509.go

Lines 818 to 829 in aedf298

	func checkSignature(algo SignatureAlgorithm, signed, signature []byte, publicKey crypto.PublicKey, allowSHA1 bool) (err error) {
	var hashType crypto.Hash
	var pubKeyAlgo PublicKeyAlgorithm
	for _, details := range signatureAlgorithmDetails {
	if details.algo == algo {
	hashType = details.hash
	pubKeyAlgo = details.pubKeyAlgo
	}
	}
	switch hashType {

What did you expect to see?

The for of the checkSignature function requires an early break

	for _, details := range signatureAlgorithmDetails {
		if details.algo == algo {
			hashType = details.hash
			pubKeyAlgo = details.pubKeyAlgo
			break
		}
	}

What did you see instead?

If this needs to be fixed, I'd be happy to submit a pr

[seankhliao]

cc @golang/security

[rolandshoemaker]

Adding a break seems reasonable, there should only ever be a single matching algorithm and this doesn't need to be constant time. Feel free to send a CL, although be aware that since we are in the freeze window at the moment, your change will not be merged until ~August, when the tree re-opens for 1.20 changes.

[gopherbot]

Change https://go.dev/cl/407215 mentions this issue: crypto/x509: optimize the performance of checkSignature